1. Field of the Invention
The present invention relates to the production of a catalyst suitable for producing an olefin polymer having a high bulk density, an excellent powder flowability, and a superior mechanical strength. More specifically, it relates to a process for producing a catalyst carrier for an olefin polymerization which is spherical in shape, has a narrow distribution of particle size, and enables the average particle size to be set to any desired size. Furthermore, the present invention relates to a process for producing a catalyst carrier for an olefin polymerization capable of producing the catalyst carrier for an olefin polymerization by an easy procedure in an industrially advantageous manner.
2. Description of the Related Art
Numerous proposals have been made regarding catalysts for an olefin polymerization composed of a transition metal compound catalyst component and an organometallic compound catalyst component.
When a transition metal compound carried on a spherical carrier having a narrow distribution of particle size is used as the transition metal compound catalyst component, it is known that a superior flowability and a high bulk density can be imparted to the resultant olefin polymer and, therefore, it is advantageous in the process.
Further, when the yield of the olefin polymer per transition metal compound catalytic component is sufficiently large, the resultant olefin polymer has little content of the transition metal and therefore, it becomes possible to eliminate the deash treatment step.
Accordingly, when the transition metal compound catalyst component having a spherical shape and having a narrow distribution of particle size has a suitable particle size and further when the yield of the olefin polymer per transition metal compound catalyst component is sufficiently large, the resultant olefin polymer has both a sufficient size and a shape exhibiting a superior flowability, and therefore, it becomes possible to eliminate the granulation step which have increased the production cost up to now.
In general, in order to eliminate the granulation step, it is desirable that the produced polymer has a spherical shape, a narrow distribution of the particle size and a suitable average particle size. When the average particle size is too small, the polymer will easily aggregate when the polymer includes a viscous component and, further, sometimes there will be problems in eliminating the granulation step. When the average particle size is too large, the polymer transporting line will easily become clogged. To obtain a polymer satisfying these conditions, the catalyst carrier for the olefin polymerization preferably has a spherical shape and a geometric standard deviation .alpha. of the particle size of not more than 1.5. Further, in accordance with the performance of the catalyst and the process of production of the polymer, the average particle size of the catalyst may be preferably set within the range from 1 to 200 .mu.m. Such a catalyst component can be easily obtained from a spherical carrier having the shape and particle size equivalent or similar to those of the desired catalyst component.
Several methods for obtaining such a catalyst carrier for an olefin polymerization are known. For example, Japanese Unexamined Patent Publication (Kokai) No. 49-65999 proposes to use spherical particles obtained from a molten hydrated magnesium halide by a spray dry method as a catalyst carrier for an olefin polymerization. In this method, the distribution of the particle size of the resultant carrier is wide, and therefore, classification becomes required. Further, when performing classification, the yield drops. Also, the resultant polymer particles become porous, and therefore, there is the problem of an insufficient mechanical strength.
As another method for obtaining a catalyst carrier for an olefin polymerization, Japanese Unexamined Patent Publication (Kokai) No. 55-13512 proposes a method of rapidly cooling a suspension obtained by stirring a molten complex compound of magnesium halide and an alcohol in an organic liquid medium. In this method, a suspension in which the disperse phase particles are repeatedly separated and joined is withdrawn and cooled to a solid, and therefore, the distribution of the particle size becomes broader and the yield is decreased during the classification.
As another method for obtaining the catalyst carrier for an olefin polymerization, Japanese Unexamined Patent Publication (Kokai) No. 56-811 proposes a method for treating a molten complex compound of magnesium halide and an alcohol in an organic liquid medium by a Lewis acid. In this method, only a carrier having a small particle size can be obtained and it is not possible to obtain a polymer having a sufficiently large size. Furthermore, since it is necessary to use a large amount of a Lewis acid, there are the problems that the cost of production of the catalyst becomes higher and further the process for treating the waste liquor becomes complicated.